Hydraulic starting system and valves therefor



May 2, 1968 1 c. JENNINGS ET AL v 3,384,027

HYDRAULIC STARTING SYSTEM AND vALvEs THEREFOR Filed Aug. 3, 1966 5 Sheets-Sheet l ATTORNEY S May 2l, 1968 L. c. JENNINGQS ET AL 3,384,027

HYDRAULIC STARTING SYSTEM AND VALVES THEREFOR Filed Aug. 5, 1966 5 Sheets-Sheet 2 HOWARD C. SPOONER BY l m ATTORNEYS May 2l, 1968 HYDRAULIC STARTING SYSTEM AND VALVES THEREFOR Filed Aug. 5, 1966 L.. C. JENNINGS ET AL- 5 Sheets-Sheet 3 32 33C 325e BQ 35C 33:57

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ATTORNEYS United States Patent Ofce 3,334,627 Patented May 2l., 1968 3,334,027 HYDRAULIC STARTING SYSTEM AND VALVES THEREFGR Lyston C. Jennings and Howard C. Spooner, Watertown,

NY., assignors to General Signal Corporation, a corporation of New York Filed Aug. 3, 1966, Ser. No. 569,921 8 Claims. (Cl. lr03-162) This invention relates to hydraulic starting and pumping systems.

U.S. Patents 3,203,165, granted Aug. 3l, 1965, and 3,234,889, granted Feb. 16, 1966, disclose systems of this kind which employ overcenter motor-pump units and which use an accumulator as the source of motive fluid for the starting operation. In each of these systems, the positioning mechanism for the displacement control element of the motor-pump unit includes a fluid pressure control motor, a pressure responsive control valve having supply and exhaust positions in which it connects the control motor with the high pressure side of the system and the reservoir, respectively, and an actuating motor which is controlled by the engine start valve and which acts on the control valve in aid of its normal pressure reaction surface. During the starting cycle, the start valve connects the actuating motor with lthe high pressure side of the system for the purpose of holding the control valve in its supply position. On the other hand, during the pumping operation, the start valve vents the actuating motor and thereby allows the control valve to perform its normal supply and exhaust functions.

Experience with these prior systems indicates that if the start valve is ymaintained open, and consequently the actuating motor is maintained in communication with the high pressure side of the system, after either the accumulator is depleted of oil or the engine becomes self-sustaining, the displacement control element of the motor-pump unit will oscillate rapidly between large displacement positions at opposite sides of the zero displacement position. The reason for this is that each of the events just mentioned causes a sudden, drastic reduction in the pressure in the high pressure side of the system which makes it impossible for the actuating motor to hold the control valve in its supply position. As a result, the control valve shifts to its vent position, the pressure in the control motor is suddenly dissipated, and the positioning mechanism rapidly moves the displacement control element over center. At this time, the motor-pump unit commences to discharge fluid to the high pressure side of the system and to raise its pressure. When the pressure is restored to the level required to enable the actuating motor to reposition the control valve in its supply position, the control motor is suddenly subjected to the full pressure then existing in the high pressure side of the system. Therefore, this motor rapidly shifts the displacement control element back to the other side of the zero displacement position and again reverses the direction of flow through the motor-pump unit. In cases where the engine is running, oscillation of the displacement control element continues until the start valve is closed and the control mechanism is set to hold the displacement control elemen-t at the proper side of the zero displacement position for pumping operation. On the other hand, in the case of abortive starts, wherein the engine does not attain a self-sustaining speed, the oscillation continues until the torque load imposed by the motor-pump unit brings engine to rest. In either case, the oscillations produce pressure pulsations of large magnitude throughout the entire system which create excessive stresses in, and can even cause failure of, the various hydraulic components.

The object of .this invention is to provide an improved starter system in which the severity of these oscillations of the displacement control element is greatly reduced. According to this invention, the system includes valving means for maintaining the actuating motor under the initial pressure of the accumulator from the commencement of the starting cycle until the start valve is closed. This improvement insures that the control valve will be maintained in its supply position regardless of the pressure in the high pressure side of the system, and thus absolutely prevents this valve from suddenly changing the pressure in the control motor. Now, the control motor always responds directly to the pressure in the high pressure side of the system during the starting cycle and does not produce the violent oscillations of the control element which have been encountered in the prior systems.

In the preferred embodiment of the invention, the valving means which insures proper operation of the actuating motor is incorporated in a package which also includes the engine start valve and a common actuator for the two valve units. This package may also incorporate means for insuring that the positioning mechanism for the displacement control element is set for motoring operation before -the motor-pump unit commences to develop torque. This feature precludes the undesirable momentary reverse rotation of the engine at the instant the start cycle is initiated which can be encountered with the prior systems. The packaged arrangement of the start valve and the valve lmeans which controls the actuating motor is a desirable feature because it is less expensive than the alternative of providing separate valves, and, in addition, it permits the invention to be incorpora-ted in existing systems in a routine manner by regular maintenancepersonnel.

The preferred and several alternative embodiments of the invention are described herein in detail with reference to the accompanying drawings in which:

FIG. l is a schematic diagram showing a hydraulic starting and pumping system of the type disclosed in U.S. Patent 3,234,889 and incorporating one form of the present invention.

FIG. 2 is a schematic diagram of a similar starting and pumping system incorporating a second form of the invention.

FIG. 3 is a schematic diagram of the preferred valve package.

FIG. 4 is a sectional View of the actual preferred embodiment.

FIGS. 5 and 6 are sectional views taken on lines 5-5 and 6--6 of FIG. 4.

FIG. 7 is a sectional view taken on line 7-7 of FIG. 6 and FIG. 8 is a sectional view taken on lines S-S of FIG. 5 and lines 88 of FIG. 6.

The starting and pumping system shown in FIG. l is employed to start auxiliary and main turbine engines 11 and l2 and to provide hydraulic fluid under pressure to a utility circuit (not shown). The system includes an overcenter motor-pump unit 13 which is connected to drive and be driven by auxiliary engine 11, and which is provided with high and low pressure ports 14 and 15 that are connected, respectively, with main conduit 16 and reservoir 17. Motive lfluid for driving unit 13 as a motor is supplied by a` gas-charged accumulator 18 through a circuit including conduits 16a, 16h and 16 and controlled by the auxiliary engine start valve 19. When unit 13 is being driven as a pump, it draws fluid `from reservoir 17 and discharges it under pressure into conduit 16. rIhis pressurized tiuid may then ilow to, and thus recharge, accumulator 18 through conduits 161;, 16e and 16a, or pass through conduit 16d, main start valve 19 and conduit 16e to hydraulic starter 21, and thus be used as the motive fluid for starting main engine 12, or pass through conduit 16,1c to the utility circuit.

The start valves 19 and 19 are of the pilot-operated type disclosed in U.S. Patent 3,203,165, and each has a main valve which is spring biased to a closed position. When the pilot valve of either of the valves 19 and 19 is shifted from its venting to its pressurizing position by the association solenoid 19a or 19a', the connection between the piloted motor and reservoir 17 is interrupted, and this motor is connected with the conduit upstream of the start valve, that is, conduit 16a in the case of valve 19, and conduit 16d in the case of valve 19. As a result, the piloted motor shifts the main valve to open position. Venting of either piloted motor allows the spring to close the main valve.

The displacement of and direction of iiow through unit 13 is controlled by cam plate 22 which is movable in opposite directions from the illustrated neutral or Zero displacement position about the axis of trunnion 23. Cam plate 22 is biased in the counterclockwise direction by a spring-motor assembly 24 including the coil compression spring 25 and a fluid pressure piston motor 26. The cylinder 27 of motor 26 is connected to the piston 28 of a shifting motor 29 and carries a spring seat having a longitudinal extension 31 which is arranged to abut the end of cylinder 32 when the two cylinders move toward each other. This extension 31 denes a limit stop for cam plate 22 which, during the pumping operation, prevents the cam plate from moving over center, i.e., through the neutral position. The piston 28 is designed to move between the illustrated position, in which it abuts stop 33, and a second position, in which its head abuts shoulder 34, for positioning assembly 24 for motoring and pumping operatitons, respectively.

Cam plate 22 is moved in the clockwise direction about the axis of trunnion 23 against the opposing bias of assembly 24 by a Huid pressure control motor 35. Fluid is supplied to and exhausted from the working chamber 36 of this motor through a pressure responsive control valve 37 with which it is connected by conduit 38. Control valve 37 includes an inlet chamber 39 which is connected with the main conduit 16 through conduit 16g, an outlet chamber 41 which communicates with conduit 38, an exhaust chamber 42 which is connected with reservoir 17, and a sliding valve spool 43. This valve spool has supply and exhaust positions and an intermediate lap position, and is biased to the illustrated exhaust position by a coil cornpression spring 44. In this position, land 45 isolates outlet chamber 41 from inlet chamber 39, and a flat 46 on land 47 provides a ow path which connects outlet chamber 41 with exhaust chamber 42. The fluid pressure in chamber 39 acts upon the left end of spool 43 and serves to shift this member to the right, first to a lap position in which lands 4S and 47 isolate chamber 41 from the other two chambers, and then to the supply position wherein land 47 continues to block communication between chambers 41 and 42, and the Hat 48 extending across land 49 connects outlet chamber 41 with inlet chamber 39.

The pressure in inlet chamber 39 required to hold valve spool 43 in the lap position against the opposition of spring 44 is termed the reference pressure, and valve 47 includes two devices for changing this pressure. The first, which raises the reference pressure, comprises a movable spring seat 51 for spring 44, and a piston motor which includes the right side of seat 51 and a working chamber 52. When working chamber 52 is vented, seat 51 assumes the illustrated low spring-load position, and, when the working chamber is pressurized, the seat is moved t the left to a high spring-load position defined by stop 53. A conduit 54 connects working chamber 52 with the pilot valve portion of main engine start valve 19', so that this chamber is vented and pressurized whenever the start valve 19 is closed and opened, respectively. The second device for changing the reference pressure acts to lower it from the normal value, and it comprises a piston motor 55 including the piston 56 which abuts the left end of spool 43, and a Working chamber 57. The Working chamber 57 is connected with the pilot valve portion of auxiliary engine start valve 19 through a pair of conduits 58 and 59 and the valving device 100 provided by the present invention. As will appear below, this chamber 57 is continuously subjected to the initial pressure in accumulator 18 whenever valve 19 is open and, at all other times, it is vented to reservoir 17.

The piston 56 of motor 55 also serves as the valve spool of a selector valve 61 which simultaneously vents and pressurizes the Working chambers 26a and 29a of motors 26 and 29. This valve comprises the inlet chamber 39 of control valve 47, an exhaust chamber 62 which is in continuous communication with reservoir 17, and an outlet chamber 63 which is connected with working chamber 29a through conduit 64. An axial passage 28a in piston 28 interconnects working chambers 26a and 29a. During pumping operation, selector valve 61 assumes the illustrated position wherein land 65 blocks communication between chambers 62 and 63, and the flat 66 extending across land 67 interconnects chambers 63 and 39. During the starting operation, valve 61 shifts to the right to a position in which land 65 blocks communication between chambers 63 and 39, and the ilat 68 extending across land 69 connects outlet chamber 63 with exhaust chamber 62. Thus, selector valve 61 vents and pressurizes the motors 26 and 29 during the pumping and motoring operations, respectively. Since the diameter of the end land 56 of piston 56 is greater than the diameter of lands 65 and 67, piston 56 will always shift to the right when the pressures in working chamber 57 and inlet chamber 39 are equal.

The valving device provided by the present invention includes a pair of ports 101 and 102 which are connected, respectively, with conduits 59 and 58, and which are interconnected by passage 103 containing spring biased check valve 104. Check valve 104 is oriented to permit flow from conduit 59 to conduit 58, but to block ow in the reverse direction. Valving unit 100 also includes an exhaust port 105 which is in continuous communication with reservoir 17 and which is connected with port 102 by a passage 106 containing a second spring biased check valve 107. The biasing spring 108 of this check valve has a movable seat 109 which is carried by the armature of a solenoid 111 so that the closing bias acting on the check valve changes yas the solenoid is ene-rgized and de-energized. Solenoid 111 is connected in parallel with the solenoid 19a of auxiliary engine start valve 19 in an energization c-ircuit which includes battery 112 and which is controlled by the manually operated start switch 113 and a speed control-led switch 114 that responds to the speed of engine 11.

Operation Since U.S. Patent 3,234,889 contains a complete description of the operation of the system shown in FIG. l, and the improvements provided by the present invention affect only the motoring mode of operation, 4the following description of operation will treat only the starting cycle of engine 11.

Before commencement of the s'tarting cycle, accumulator 18 is precharged with gas at 'a pressure of 1500 p.s.i. and is then charged with oil by a hand pump circuit (not shown). It is assumed that the fully charged pressure of the accumulator is 3000 p.s.i., and that the three reference pressures of contr-ol valve 37 are 1500 p.s.i., 3000 p.s.i. and 4000' p.s.i.

In order to start auxiliary engine 11 the operator closes switch 113 to energize solenoid 19a and open start valve 19. This permits uid from the accumulator 18 to flow into the high pressure port 14 of the motor-pump unit through conduits 16a, 16b and 16, and also permits fluid at accumulator pressure to pass to the working chamber 57 of motor 5S through the pilot portion of valve 19, conduit 59, port 101, passage 103, check valve 104, port 102 and conduit 58. Since solenoid 111 is energized simultaneously with solenoid 19a, the load in spring 108 is now sufficient to keep check valve 107 closed and prevent bleed oif of the -pressure in working chamber 57. The pressure of 3000 p.s.i. in this chamber causes motor 5S to shift selector valve 61 to a position in which it vents motors 26 and 29, and to shift control valve 37 to its supply position in which control motor 35 is connected with main conduit 16. As a result, control motor 35 moves cam plate 22 in the clockwise direction to its maximum displacement position at the motoring side of neutral and maintains it in that position against the opposing bias of spring 25.

The fluid delivered to motor-pump unit 13 causes it to develop torque and accelerate engine 11. As the engine accelerates, the pressure of the fluid delivered by accumulator 18 progressively -decreases from its initial value of 3000 p.s.i. However, this change in pressure is not reected in working chamber 57 because the check valve 104 closes as soon as the pressure in conduit 59 begins to drop below the initial charge pressure of the accumulator. Therefore, as long as solenoid 111 is maintained energized and check valve 107 is held closed, the pressure in working chamber 57 remains at 3000 p.s.i. and valves 37 and 61 remain in their supply and vent positions, respectively. Because of this, the pressure in working chamber 36 of control motor 35 will be substantially the same as the pressure in main c-onduit 16 throughout the starting cycle.

Under normal conditions, engine 11 will have been ignited and ywill have achieved self-sustaining operation before accumulator pressure decreases to 1500 p.s.i. and the accumulator is depleted of oil. Since control motor 35 is dimensioned to hold cam plate 22 in the maximum displacement position as long as the pressure in its working chamber 36 is above 1500' p.s.i. it follows that the cam plate 22 in the normal case will not move away from its maximum displacement position during the starting cycle. When the engine reaches a self-sustaining speed, switch 114 automatically opens the holding circuit fo-r switch 113 and allows this switch in turn to open and de-energize solenoids 19a and 111. De-energization of solenoid 19a allows auxiliary engine start valve 19 to close and interrupt the flow of fluid from the accumulator 18 to high pressure port 14. On the other hand, de-energization of solenoid 111 reduces the load inl spring 108 and permits check valve 107 to open under the action of pressurized oil trapped in working chamber 57. Therefore, this oil may now escape to reservoir 17 through conduit 58, port 102, passage 106 and port 105. Since engine 11 is now driving motor-pump unit 13 as pump, and cam plate 22 is still at the motoring side of the neutral position, unit 13 will commence to evacuate main conduit 16. As a result, the pressure in this conduit and in the working chamber 36 of control motor 35 will decrease well below 1500 p.s.i., and spring 25 will move cam plate 22 in the counterclockwise direction to a small displacement position at the pumping side of the neutral position. At the same time, spring 44 will return valves 36 and 61 to their illustrated vent and supply positions, respectively. As soon as cam plate 22 moves over center, unit 13 commences to discharge oil under pressure to conduit 16 and thus quickly restores its pressure to 1500 p.s.i. As this is happening, selector valve 61 transmits system pressure to shifting motor 29 and causes it to move the spring-motor assembly 24 to its pumping position wherein the stop defined by extension 31 is eifective to prevent the cam plate 22 from moving back to the motoring side of neutral. Cam plate 22 will now assume a position in which the displacement of unit 13 is equal to the rate of leakage from the system. At this time the pressure in inlet chamber 39 of valve 37 will move spool 43 to its lap position.

In the `abnormal case, where accumulator 18 is given an inadequate gas precharge or is charged with an insufficient quantity of oil for a start cycle, the engine 11 does not achieve a self-sustaining speed by the time accumulator 18 is depleted of oil. When this happens, the engine 11, which has considerable momentum, will commence to coast and drive unit 13 as a pump. Since cam plate 22 is at the motoring side of neutral position, unit 13 will draw fluid from conduit 16 and discharge it to reservoir 17. This pumping action will quickly decrease the pressure in conduit 16 toward zero. In the prior system of Patent 3,234,889, wherein conduit 58 is in constant, direct communication with conduit 59, this change in pressure causes valves 37 and 61 to shift to their exhaust and supply postiions, respectively. This 'action resulted in sudden venting of working chamber 36, and in sudden pressurization of working chambers 26a and 29a, and caused the controls for cam plate 22 to move it rapidly to a large, and perhaps even the maximum, displacement position at the pumping side of neutral. Uni-t 13 would then commence to discharge oil to conduit 16 and recharge accumulator 18. As soon as the pressure in conduit 16 was restored to 1500 p.s.i., valves 37 and 6-1 would shift back to their supply and vent positions, respectively, and suddenly apply full system pressure to working chamber 36 and vent working chambers 26a and 29a. Now the controls would shift cam plate 22 rapidly back to a rather large displacement position at the motoring side of neutral. At this point, unit 13 would again commence to act as a motor and drive engine 11. However, as soon as accumulator 18 was again depleted of oil, `the controls would produce another violent oscillation of cam plate 22. T-hese oscillations continued until the engine 11 came to rest, and, since they were accompanied by severe pressure pulsations in the conduits connected with ports 14 and 15, there was ample opportunity for the system components to be damaged.

In contrast to t-his, the valving device provided by .the present invention holds the initial charge pressure of accumulator 18 in working chamber 57, and thus enables motor 55 to keep valves 37 and 61 in their supply and exhaust positions, respectively, as long as solenoid 111 remains energized. Therefore, in this system the pressure changes in conduit 16 always are reflected directly in working chamber 36, and cannot cause valve 61 to pressurize motors 26 and 29. With this arrangement, motor 35 and spring 25 still move the cam plate 22 back and forth across the neutral position during an abortive start, but the rate of movement of the claim plate and the amplitude of its oscillation `are much less than in the prior system. Actual experience with this improvement shows that it reduces to tolerable levels the pressure pulsations encountered during abortive starts.

Another abnormal case in which the invention effects an improvement concerns starts in which the switch 114 fails to open when the engine 11 reaches a self-sustaining speed. This situation produces the same effect as an abortive start, except that the unit 13 operates continuously as a pump which discharges alternately through ports 14 and 15, and, since the engine is running under its own power, the oscillations of cam plate 22 continue until start switch 113 is opened manually. As in the case of the abortive start, the valving device 100 so reduces the severity of these oscillations that the pressure pulsations are kept within tolerable limits.

The FIGURE 2 embodiment The system shown in FIG. 2 is generally the same as the one of FG. 1, except that here the valves 204 and 207, which correspond to check valves 104 and 107 embodied in the device 100 of FIG. l, are combined with the auxiliary engine start valve in a single Package 200.

assess? In this case, the passage which interconnects ports 201 and 202 has two enlarged sections 203m and 203b, which are separated by the main poppet 215 of the start valve, and the latter section leads to a delivery port 216 as Well as to check valve 204. The elements 201, 203:1, 203b and 216 define the supply path through which motive Huid is delivered to the motor-pump 13. The main poppet 215 is urged toward its seat 217 by a coil compression spring 218 and by the iluid pressure in a pilot chamber 219` which acts upon its upper surface 221. The poppet is shifted in the opening direction against this bias by the pressure in passage section 203e which acts upon the annular shoulder 222. Pilot chamber 213 is connected with inlet port 201 by passage section 203e and a restricted passage 223 formed in the poppet, and is connected with exhaust port 205 through a path comprising passages 224 and 225 and controlled by a pilot valve in the form of spring biased check valve 226. This check valve is oriented to normally block flow from pilot chamber 219, but is opened by push rod 227 whenever solenoid 211 is energized to hold valve 207 closed.

The valving package 200 is incorporated in the system by connecting ports 202 and 205 with conduit 53 and reservoir 17, respectively, by connecting port 201 directly with accumulator 18 through conduit 16a, and by connecting port 216 with the conduits Mb and 16 leading to the high pressure port 14 of motor-pump unit 13. This last mentioned connection includes a check valve 223 which permits tlow from, but not into, passage section 203b. When the FIG. 2 system is in a standby condition, solenoid 211 is de-energized and valves 204i, 207 and 226 assume their illustrated positions. Although the fluid in passage section 203e is subjected to the full charge pressure of accumulator 13, and thus tends to open main poppet 215, the uid in pilot chamber 219 is under the same pressure and acts on a larger reaction surface, namely upper surface 221. Therefore, the net pressure force acting on the poppet 215 supplements the biasing force developed by spring 21S and holds poppet 215 tightly against its seat 217. This precludes leakage from accumulator 18.

In order to start engine 11, the start switch (not shown) is closed to energize solenoid 211 and cause it to close and open the valves 207 and 22e, respectively. Opening of valve 226 allows oil to escape from pilot chamber 219 to reservoir 17 at a rate greater than that at which it can enter this chamber through restricted passage 223. As a result, the pressure in chamber 219 de` creases below that in passage section 203e, and the net pressure force acting on poppet 215 shifts this member to open position against the opposition of spring 218. Fluid under accumulator pressure now is delivered to the high pressure port 14 of unit 13 via passage section 203i?, port 216, and conduits 16h and 16, and -to the working chamber 57 of actuating motor 55 through passage section 203b, check valve 204, port 202 `and conduit 5S. The FlG. 2 system now eifects starting of engine 11 in the same way as the FIG. 1 system.

During a normal starting cycle, solenoid 211 is deenergized as soon as engine 11 becomes self-sustaining. Therefore, at this time, valves 207 and 226 are allowed to open and close, respectively. As soon as valve 226 closes, the pressures in chamber 219 and passage section 203e equalize, and main poppet 215 closes. Simultaneously, opening of valve 207 automatically sets the controls for unit 13 to their pumping condition. Therefore, this unit can now recharge the accumulator 13 and perform its other pumping functions. In the case of an abortive start or a failure of switch 114, the valving device 200 serves to prevent violent oscillations of the cam plate of unit 13 in the same way as its counterpart in FIG. 1. While the Icyclic variations in the pressure in conduit 16h during these conditions are reflected in passage section 203:1, and may cause closing and opening movement of main poppet 215, this will not adversely aifect the performance of the motor-pump unit 13 or the starting system.

The preferred embodiment The preferred valving device 300, which is illustrated schematically in FIG. 3, is similar to device 200 in that it incorporates the start valve and the check valves necessary to trap fluid in actuator motor 55. However, in this embodiment, the path between the pilot chamber 319 of the start valve and exhaust port 305 includes a ow restrictor 329, and the inlet and outlet ports 301 and 302 are interconnected by a path which comprises passages 331 and 332 and which is controlled by check valve 333 rather than main poppet 315. The check valve 333 normally blocks flow from port 301 to port 302, but is mechanically unseated to permit such flow by an actuating rod 334 which is operated by solenoid 311. Thus, when the solenoid is energized to eifect opening of pilot valve 326 and closure of the vent valve307, it simultaneously opens valve 333 and permits fluid under accumulator pressure to iiow to the actuating motor through a path comprising port 301, passages 332 and 331, valve 304, outlet port 302 and conduit 58.

1t will be observed that, since spring 25 in motor-pump unit 13 biases cam plate 22 to a position at the pumping side of neutral when the starting system is at rest, unit 13 will momentarily rotate engine 11 in the reverse direction at the commencement of the starting cycle if it `commences to develop torque before the controls have been energized to move the cam plate over center. The preferred embodiment eliminates this condition, This is accomplished by so sizing ow restrictor 329 that, when valves 326 and 333 are irst opened, iluid under accumulator pressure is transmitted to outlet port 302 before the pressure in pilot chamber 319 can decrease suiiiciently to permit opening of main poppet 315. As a result of this delay, actuating motor 55 will have time to shift valves 37 and 61 to the positions required for motoring operation before high pressure port 14 is subjected to full accumulator pressure. Since shifting of these valves vents motors 26 and 29 and places motor 35 in direct communication with conduit 16, and since the pressure required by motor 35 to shift the cam plate over center is much less than the pressure required by unit 13 to satisfy the breakaway torque requirement of engine 11, it should be apparent that, when main poppet 315 opens and the pressure in conduit 16 rises, motor 35 will move the cam plate to the motoring side of neutral before the unit 13 commences to rotate. Thus, the valving device 300 precludes any reverse rotation of engine 11.

It should be noted that since outlet port 302 in the FIG. 3 embodiment is isolated from the high pressure conduit 16b when solenoid 311 is de-energized, systems incorporating this form of the invention do not require the check valve 228 used `in FIG. 2.

The `details of the actual valving device 300 are shown in FIGS. 4 8, wherein the counterparts of the components shown in FIG. 3 are, as far as possible, identied by the same reference numerals. While the construction of this embodiment will be apparent from an inspection of these gures, it will be helpful to describe specifically the following ow paths shown schematically in FIG. 3:

(1) The path connecting inlet port 301 with check valve 333 is shown in FIG. 4 and comprises annular groove 303a formed in the outer periphery of sleeve 33S, drilled housing passage annular housing chamber 322b, longitudinal passage 332e defined by a at on the outer periphery of sleeve 336, and radial passages 332d and 332e.

(2) The path connecting check valve 333 with port 302 is shown in FIGS. 4 and 5 and comprises axial passage 331a formed in block 337, drilled passage 331i, annular housing groove 331C, drilled housing passages 331e', 331e and 331f, axial passage 331g formed in the seat sieeve 338, check valve 304, and the axial passage 331.1: formed in tting 339.

(3) The path connecting outlet port 302 with exhaust port 305 is shown in FIGS. 5-8 and comprises axial passage 331h, radial passages 306:1 and 306b, longitudinal passage 306C defined by a flat on the outer periphery of sleeve 341 (see FIG. 5), annular housing chamber 306d, drilled housing passage 306e, housing chamber 306f (see FIGS. 6 and 8), slot 306g formed in plug 342, axial passage 306k in seat block 343, check valve 307, radial passages 306i and 306]' formed in sleeve 344, chamber 306k, drilled passage 3061, annular housing chamber 306m, and drilled housing passage 30611 (see FIG. 7).

(4) The path connecting pilot chamber 319 with eX- haust port 305 is shown in FIGS. 4 and 7 and comprises slot 32551 formed in spring seat 345, check valve 326, chamber 325b yformed in insert 346, drilled passages 325C and 325d formed in block 347, annular housing chamber 325e, and drilled housing passage 30611. In this embodiment, either passage 325a or passage 3250i may serve as the flow restrictor 329 of FIG. 3.

Although we have referred to two specific starting systems in which the invention may be used, it should be understood that there are other types of hydraulic starting systems which present the problem which the invention solves. One such system which deserves mention is disclosed in U.S. Patent 3,106,057, granted Oct. 8, 1963. In cases where the cam plate of the motor-pump unit in this prior system is provided with an unbalanced control, i.e., a control which automatically moves the cam plate to a pumping position rather than the neutral position when the accumulator is fully discharged, intolerable oscillations of the cam plate can occur under the two abnormal conditions mentioned earlier. The severity of these oscillations can be reduced by incorporating the present valving device in conduit 75 of the patent so that it` serves to' maintain motor 53 at the initial charge pressure of the accumulator throughout the starting cycle.

As stated previously, the drawings and description relate only to the preferred and several alternative embodiments of the invention. Since the structures of the these embodiments can be changed in many respects without departing from the inventive concept, the following claims should provide the sole measure of the scope of the invention.

What We claim is:

r1. A hydraulic starting and pumping system comprising (a) .an overoenter motor-pump unit having high and loW p-ressure ports and a displacement control element which is movable between positions at opposite sides of a zero displacement position to reverse the ydirection of iiow through the unit;

(b) an accumulator for supplying motive fluid to the rnotor-pump unit to drive same as a motor;

(c) first conduit means connecting the accumulator with the high pressure port and controlled by a start valve;

(d) a -uid reservoir;

(e) pressure actuated means for positioning the displacement control element and including a fluid pressure motor, a valve having supply and exhaust positions in which, respectively, it connects the motor with the 'high pressure port and the reservoir, and yan actuating motor for holding the valve in one of its positions during the starting cycle;

(f) second conduit means connecting the actuating motor with the rst conduit means;

(g) means for permitting ow from the accumulator to the second cond-uit means only when the start valve is open;

(h) means for preventing flow from the motor-pump unit to the -second conduit means;

(i) a check valve in the second conduit means oriented to prevent ow from the actuating motor;

'(j) third conduit means connecting the actuating motor with the reservoir;

(k) a vent valve control-ling the third conduit means;

and-

(l) actuating mean-s which closes and opens the vent valve as it opens and closes, respectively, the start valve.

2. A system as defined in claim 1 wherein the means for permitting and preventing flow to the second conduit means comprises a valve which is operated in unison with the start valve and which isolates the second conduit means from the first conduit means when the start valve is closed.

3. A system as defined in claim 1 wherein (a) the second conduit means is connected with the first conduit means between the start valve and the high pressure port, whereby the start valve serves as Isaid means for permitting flow to the second conduit means; and

(b) said means for preventing flow to the second cond-uit means comprises a check va=1ve interposed in the first conduit means between the high pressure port and the junction with the second conduit means.

4. A system as defined in claim 1 wherein (a) the start valve has a main portion which controls flow from the accumulator to the high pressure port of the motor-pump unit, and a piloting portion which controls the operation of the main portion; and

(b) the actuating means includes mechanical means which simultaneously operates both the piloting portion of the start valve and the vent valve.

5. A system as defined in claim 4 wherein (a) the second conduit means is connected with the first conduit means between the main portion of the lstart valve and the accumulator, whereby the main portion of the start valve serves as said means for preventing flow from the motor-pump unit to the second conduit means; and

(b) said means for permitting ow from the accumulator to the second conduit means comprises a second valve interposed in the second conduit means between the check valve and the junction with the first conduit means and which is .opened and closed by said mechanical means as the latter closes and opens, respectively, the vent valve.

6. A system as defined in claim 4 wherein (a) the second conduit means is connected with the first conduit means between the main portion of the :start valve and the high pressure port, whereby the main portion of the start valve serves as said means for permitting ow from the 4accumulator to the `second conduit means; and

(b) said means for preventing flow from the motorpump unit to the second conduit means comprises a check valve interposed in the first conduit means between the high pressure port and the junction with the second conduit means.

7. A system as defined in claim 5 which includes means for reta'rding opening of the main portion of the start valve so that when the actuating means open-s the second valve and closes the vent valve the pressure in the actuating motor increases at a faster rate than the pressure at the high pressure port.

8. .A system as defined in claim 5 wherein the star-t valve comprises' (a) a main portion that controls flow from the accumulator to the high pressure port and which is spring biased to a closed position;

(b) a first reaction surface on the main portion which is subject to accumulator pressure and which urges the main portion in the opening direction;

(c) a piloting chamber connected with the `accumulator through a first restricted passage;

(d) a second reaction surface on the main portion which is subject to the pressure in the piloting chamber and is arranged to develop a force which urges the main portion in the closing direction;

l i (e) a second restricted passage connecting the piloting References Cited chamber with the reservoir; and (f) a pilot valve operated by the mechanical means UNHED STATES PATENTS for opening and closing the second restricted passage 3,203,165 8/1965 Pal-tr 6()* 18 as the mechanical means closes and opens, respec- 5 3 234 726 2/1966 Hann 103 162 X tively, the Vent valve: n (g) the flow restriction afforded by the second restricted 3234889 2/1966 Cooper et al 10s-38 passage being greater than the restriction to flow DONLEY I STOCKING Primary Examiner from the accumulator to the actuating motor through the second conduit means. 10 WILLIAM L. FREEH, Examiner. 

1. A HYDRAULIC STARTING AND PUMPING SYSTEM COMPRISING (A) AN OVERCENTER MOTOR-PUMP UNIT HAVING HIGH AND LOW PRESSURE PORTS AND A DISPLACEMENT CONTROL ELEMENT WHICH IS MOVABLE BETWEEN POSITIONS AT OPPOSITE SIDES OF A ZERO DISPLACEMENT POSITION TO REVERSE THE DIRECTION OF FLOW THROUGH THE UNIT; (B) AN ACCUMULATOR FOR SUPPLYING MOTIVE FLUID TO THE MOTOR-PUMP UNIT TO DRIVE SAME AS A MOTOR; (C) FIRST CONDUIT MEANS CONNECTING THE ACCUMULATOR WITH THE HIGH PRESSURE PORT AND CONTROLLED BY A START VALVE; (D) A FLUID RESERVOIR; (E) PRESSURE ACTUATED MEANS FOR POSITIONING THE DISPLACEMENT CONTROL ELEMENT AND INCLUDING A FLUID PRESSURE MOTOR, A VALVE HAVING SUPPLY AND EXHAUST POSITIONS IN WHICH, RESPECTIVELY, IT CONNECTS THE MOTOR WITH THE HIGH PRESSURE PORT AND THE RESERVOIR, AND AN ACTUATING MOTOR FOR HOLDING THE VALVE IN ONE OF ITS POSITIONS DURING THE STARTING CYCLE; (F) SECOND CONDUIT MEANS CONNECTING THE ACTUATING MOTOR WITH THE FIRST CONDUIT MEANS; (G) MEANS FOR PERMITTING FLOW FROM THE ACCUMULATOR TO THE SECOND CONDUIT MEANS ONLY WHEN THE START VALVE IS OPEN; (H) MEANS FOR PREVENTING FLOW FROM THE MOTOR-PUMP UNIT TO THE SECOND CONDUIT MEANS; (I) A CHECK VALVE IN THE SECOND CONDUIT MEANS ORIENTED TO PREVENT FLOW FROM THE ACTUATING MOTOR; (J) THIRD CONDUIT MEANS CONNECTING THE ACTUATING MOTOR WITH THE RESERVOIR; (K) A VENT VALVE CONTROLLING THE THIRD CONDUIT MEANS; AND (L) ACTUATING MEANS WHICH CLOSES AND OPENS THE VENT VALVE AS IT OPENS AND CLOSES, RESPECTIVELY, THE START VALVE. 